1. Field of the Invention
The present invention relates to the field of optical and magnetooptical information storage systems and, more particularly, to a waveguide type of integrated magnetooptical read/write head, which flies on the air bearing at a disk surface for high density recording and reading of information onto and from a storage media, as in a disk drive.
2. Description of the Related Art
Information storage systems, particularly those used with computer systems, typically store data magnetically or optically onto a storage media, a rotating magnetic or optical disk, for example. Such storage media may include an information memory media for document files, computer memories and the like, which are used for recording and retrieval only, or media which-permits recording, retrieval or erasure of information. The data stored on such media, whether magnetic or optical, is contained in tracks on the media. Once formatted on a disk, such tracks are spiral or concentric about the disk center and may number in the thousands of tracks per disk side. The total number of tracks per disk surface and, hence, the storage capacity of the disk, then depends on the diameter of the disk utilized and the track and bit density. The method of recording, either magnetically or magnetooptically, determines the size of the magnetic domains being recorded. The size of the magnetic domain determines the track density and the bit density, which in turn controls the quantity of data which can be recorded in a given area.
In both magnetic recording and magnetooptical recording, a thin film magnetic layer near the surface of a disk is magnetized in one of two directions. Information is stored in the magnetic domains of this magnetic layer along tracks by reversing the orientation of the magnetization of the magnetic domains in the layer at given points along the track a the disk rotates. Recording heads on either linear or rotary actuators are used for this purpose. Recording and reading may be done using the same head or with different heads. Where recorded information (data) is to be changed from time to time, read/write heads are employed.
In magnetooptical recording, the magnetic media is heated by a light spot to a temperature such that perpendicular magnetic recording is easily accomplished at those heated spots. Information is encoded and is stored in a sequence of magnetic domains along a track in the magnetic layer. The domain magnetization is oriented substantially normal to the surface of the disk or storage media surface, in either of two possible orientations, north pole up or north pole down, for example, depending upon the direction of the applied magnetic field.
In a prior art optical and magnetooptical media reading apparatus, such as seen in FIG. 1, an optical head assembly, controlled and supported adjacent the media surface by an actuator, is positioned and focused on a track so that reading may take place. In the reading mode, the optical head assembly focuses a light beam on a domain on the data storage media in a nominally track centered position. Typically the light beam is a laser beam which is generated by a semi-conductor laser. The Kerr rotation of the plane of polarization of the light beam reflected from that spot, indicates the magnetization of the magnetic domain at that location on the disk. The reflected light beam with polarization rotated is then coupled or projected onto a photodetector, producing a signal indicative of the state of magnetization. This signal is then processed with other such signals in succession to extract the recorded information.
In FIG. 1, a differential type of magnetooptical information reading system is employed. To this end a light beam 1 emitted by a semi-conductor laser 2 which is linearly polarized in the plane of the paper, for example, is then collimated by a collimating lens 4. The linearly polarized, collimated light beam 1 passes through a beam splitter 6. The light beam 1 is then focused as a spot on a magnetooptical recording media 8 by an objective lens 10. A magnetic domain 12 at that spot on the media which reflects the light beam I, interacts with the light beam to rotate the plane of polarization expressed as+or -.theta.K, as determined by the magnetization of the magnetic domain 12 in the magnetic layer.
The polarization rotated, reflected light beam is nominally collimated by the objective lens 10 and is reflected by the beam splitter 6, whereafter it is optically focused as a converging light beam 1a by a lens 16. The converging beam 1a is divided by a polarizing beam splitter 18 with the divided, separate light beams 1b and 1c then passing through a pair of analyzers 20, 22, respectively, to be detected as intensity modulated light beams 1d, 1e, by a pair of photodetectors 24, 26, respectively.
Efforts to reduce the size and weight of optical heads are represented by optical integrated circuits or thin film structures, one type of which is found in FIG. 1 of U.S. Pat. No. 4,911,512 which is represented in FIG. 2 herein. In FIG. 2, there is shown a far-field type of optical transducer 30. A semi-conductor laser 32 is secured on a submount 33 of silicon, for example. A thin film silicon dioxide, SiO.sub.2, waveguide element 34 and a glass waveguide layer 36 are also fixed on the submount 33. On the glass waveguide layer 36, there are formed a collimator lens 36, a beam splitter 38 and a focusing grating coupler 40. A light beam 1 emitted by the laser 32 enters the waveguide layer 36 at one of the end faces thereof. The light beam 1 is collimated by the lens 36 and concentrated or focused by the focusing grating coupler 40, at a point 42, projected as a spot on a disk surface (not shown). Light reflected from the spot on the disk returns through the focusing grating coupler 40 into the waveguide 36 and is directed by the beam splitter 38 to an optical sensor 44 located on one side of the waveguide 36 so that information recorded on the disk is read.
As seen in FIG. 3 herein, which is a representation of FIG. 5 in European patent application, publication number 0 338 864 A2, published Oct. 25, 89, effort has been directed towards providing a thin film magnetooptic head 50 which is mounted on a slider 52, to provide near-field optical coupling with a recording medium 54. The slider 52, as described in this patent application, flies on an air bearing, i.e., the air which moves with the media surface as the media 54 moves or, if a disk, rotates. A light beam generated by a light source 56 is guided through an optical waveguide 58 to the recording medium 54, where it is reflected back through the waveguide 58, to a point at a waveguide intersection, or overlap, 60 where a portion of the reflected light is projected through a second optical waveguide 62 which is optically coupled to a photodetector 64 provided at the end of the second optical waveguide 62. By providing a polarizer 66 on the first optical waveguide 58 and an analyzer 68 on the second optical waveguide 62, the rotation of the polarization of the light beam can be sensed, from which the information, recorded in the form of magnetic domains (not shown) in the magnetic medium 54, can be determined.
As described in the referenced patent application and as seen in FIGS. 7, 18 and 19 therein, this thin film magnetic head 50 includes a magnetic recording section. This magnetic recording section, comprises an electromagnet which has a thin film magnetic circuit defining an air gap adjacent to and paralleling the media surface. A thin film coil links this magnetic circuit. The magnetic circuit defines an air gap adjacent to the media surface for recording magnetic domains poled in the magnetic layer in a plane paralleling the media surface. Magnetic recording, as discussed in this patent application, is the same as that ordinarily performed by an induction head, which from the description in this patent application, involves no use of the optical system for heating of the magnetic media at the time of recording or at the location where recording is taking place. This coupled with a magnetic circuit arrangement which poles the magnetic domains in a plane paralleling the media, as seen in FIGS. 7 and 19 of that patent application negates the potential of high density recording. The description of the referenced application mentions conventional recording techniques. One convention employs a stray field for recording in a heated magnetooptic media. A second convention employs a magnetic bias field. Heating of the media is not mentioned in this second convention which appears to be the recording technique contemplated with respect to the recording heads of FIGS. 7, 18 and 19 of the referenced application.
Although vertical recording is illustrated in FIGS. 16B1 and 17B1, such recording is nowhere linked to the recording head described in the application either by direct reference or by implication.